feat(frontend+backend): add scan history diff view

[KBarathraj]

Description

Adds a Compare Scans feature. Users can select two historical scans of the same target and see findings categorized as new, fixed, unchanged, or severity changed. Helps track remediation progress over time.

Related Issues

Closes #336

issue name : Add Scan History Diff View for Comparing Historical Scan Results

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• ./testing/test_python.sh :- 9/9 passing (9 new tests for diff_service)
• cd frontend && npm run test :- passing
• cd frontend && npm run build :- zero TypeScript errors, zero new warnings
• Manual: seeded two scans, verified 200/400/404/422 responses via Swagger, verified all four diff categories render correctly in UI

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

Screenshots of changes

Before:

After :

Comparing scans:

[utksh1]

Requesting changes before merge. The scan diff feature is promising, but there are correctness issues to clean up: the frontend type has a duplicated 'before' property in SeverityChangePair, the diff fingerprint assumes every finding has title/category/target and can crash on malformed parser output, and the UI/API path needs regression coverage for missing fields and same-scan/different-target cases. Please tighten those before review.

[utksh1]

Thanks for following up. Clarifying the change request so it is actionable:

Why this is blocked:
Requesting changes before merge. The scan diff feature is promising, but there are correctness issues to clean up: the frontend type has a duplicated 'before' property in SeverityChangePair, the diff fingerprint assumes every finding has title/category/target and can crash on malformed parser output, and the UI/API path needs regression coverage for missing fields and same-scan/different-target cases. Please tighten those before review.

What to do next:

• Fix the specific issues called out above.
• Push the updated branch and make sure the relevant CI checks pass.
• Reply here when ready for re-review.

[KBarathraj]

Hey bro @utksh1, all three points have been addressed and all 6 CI checks are now passing.

SeverityChangePair : conformed clean
fingerprint() and _parse_findings() hardened with .get() fallbacks and null-byte separator
Route level integration tests added for same scan 400, different target 400, missing scan 404, and valid 200

32 tests passing total. please check it out man

[utksh1]

Re-reviewed after the latest push. Still blocked: please fix the duplicated before field in the frontend severity-change type, make diff fingerprinting tolerate missing finding fields without crashing, and add regression coverage for missing fields plus same-scan/different-target cases.

[KBarathraj]

Hi @utksh1, I've now done a complete line by line go through of every file in the commit and cannot reproduce any of the three issues you mentioned. Could you please help me understand exactly what you're seeing?
Specifically:
Which file and line number shows the duplicate before property?
Which exact line in fingerprint() or compute_diff() do you think can crash?
Which test case do you feel is missing?

I ask this because I've verified directly from git:

SeverityChangePair has always had exactly before: Finding and after: Finding
fingerprint() uses .get() with fallbacks on all three fields.
34 tests now cover missing fields, None values, same-scan 400, different-target 400, asymmetric 404 cases

A screenshot or direct quote from the Files Changed tab would help me address your concern precisely. I genuinely want to fix issue that the commit has. I just can't find it without knowing where to look.

[utksh1]

Re-reviewed after the latest push. Still blocked: please fix the duplicated frontend severity-change field, make diff fingerprinting tolerate missing title/category/target without crashing, and add regressions for missing fields plus same-scan/different-target cases.

[KBarathraj]

As stated previously,Please be more specific

[KBarathraj]

completed requested changes

[KBarathraj]

Hi @utksh1 — this is now the third review cycle with the identical three complaints word-for-word. I've checked the diff at every commit:

SeverityChangePair in api.ts has exactly before: Finding and after: Finding — no duplicate
fingerprint() uses .get("title") or "", .get("category") or "", .get("target") or "" — cannot crash
34 tests cover same-scan 400, asymmetric 404s, different-target 400, and valid-diff content

Could you paste the specific file + line number for each concern? I can't fix something I can't locate in the code.

[KBarathraj]

hey @utksh1 ,can you review this pr out

[utksh1]

Re-reviewed the latest push. Still too large/risky to merge as-is: 14 files and full-stack scan history diff behavior need a cleaner rebase and focused verification. Please rebase on main, reduce unrelated churn, and make the PR easier to validate end to end.

[utksh1]

Closing due to unresolved review feedback.